1. Field of the Invention
The present invention relates to a flash memory and, more particularly, to a re-programmable flash memory micro controller. The flash memory may be configured as a programmable logic controller.
2. Related Information
Programmable logic controllers on the market today generally have a common architecture. Typically, the controller CPU includes a microprocessor, possibly supplemented with a custom control instruction processor (boolean processor), for execution of the user program under the supervision of an operating system, random access data memory (RAM) for user and operating system data, battery backed RAM or non-volatile EEPROM for storing the user program, and a permanent ROM or EPROM for storage of the operating system software.
The user program is typically prepared on a general purpose computer and loaded into the PLC in symbolic form. The loading is typically by means of a serial communications protocol, though a removable memory cartridge may sometimes be used to by-pass this step. Within the PLC, the symbolic code is converted to executable code by a compiler. Included in the system software that must be permanently stored in ROM, there is the actual operating system that coordinates execution, the communications software to support transfer of the user program and data, and the compiler which converts the symbolic user program to executable form.
The operating system has to coordinate the communications, compilation, and program execution functions. This requires some sophistication of the operating system to respond to communications events, queue/de queue deferred tasks, and manage mode transitions between program mode and run mode. The compiler and communications software functions may be quite large, and significantly extend permanent storage requirements beyond that needed for controlling the execution of the user program.
Recently introduced models designed for low cost have used micro controllers including the data RAM and operating system ROM on a single chip with the microprocessor. The user program is contained in an external storage device: battery backed RAM, EPROM, or EEPROM, possibly added to the basic unit as a removable memory cartridge.